The invention relates to a process for the production of flexible to semi-rigid polyurethane shaped articles with a compacted edge zone of given hardness and a significantly more flexible cell core, so-called integral foams, in which non-combustible mixtures of fluoroalkanes which comprise 1,1,1,3,3-pentafluorobutane (R 365mfc) are employed as physical blowing agents.
To build up a compacted edge zone with a cellular internal structure of flexible to semi-rigid polyurethane mouldings, monofluorotrichloromethane (R 11) was used almost exclusively as the blowing agent until the ozone-damaging properties were known. Since the ozone-damaging properties of chlorinated hydrocarbons has become known, there has been no lack of attempts to employ other types of blowing agents for the production of cellular polyurethanes.
EP-A 364 854 thus describes a process for the production of shaped articles with a compacted edge zone and a cellular core, preferably shoe soles, from starting substances which are known per se but using low-boiling aliphatic and/or cycloaliphatic hydrocarbons having 4 to 8 carbon atoms in the molecule. However, a disadvantage of these blowing gases is their combustibility.
EP-A 381 986 discloses the use of C3-C5-fluoroalkanes as blowing agents in the production of polyurethane foams, and U.S. Pat. No. 5,906,999 discloses the production of flexible integral foams using 1,1,1,3,3-pentafluoropropane (R 245fa). However, it has been found that when integral foams are produced using these blowing agents, foams with an unsatisfactory integral structure are obtained.
The object of the invention was the development of a process for the production of flexible integral foams with a pronounced integral structure which is equivalent to that of products blown with CFCs or HCFCs.
It has now been found that if certain mixtures of fluorohydrocarbons are used as blowing agents, integral foams which are equivalent in respect of compressive strength and surface hardness to systems blown by R 11 or R 141 b and systems blown by hydrocarbons can be obtained. Furthermore, these mixtures are not combustible, which means a great advantage for their handling and processing.
The present invention therefore provides a process for the production of flexible to semi-rigid polyurethane shaped articles with a compacted edge zone and a flexible, cellular core, in which
a) organic and/or modified organic polyisocyanates and/or polyisocyanate prepolymers are reacted with
b) at least one polyol component with an OH number of 20 to 200 and a functionality of 2 to 6, preferably 2 to 3,
c) optionally in combination with a polyol component with an OH number of 201 to 899 and a functionality of 2 to 3, and with
d) at least one chain lengthening component with an OH or amine number of 600 to 1,850 and a functionality of 2 to 4, and with
e) optionally additives, activators and/or stabilizers which are known per se
in the presence of water and in the presence of 1,1,1,3,3-pentafluorobutane and blowing agent mixtures comprising at least one further fluoroalkane.
1,1,1,3,3-Pentafluorobutane (R 365mfc) is preferably employed as a mixture with 1,1,1,2-tetrafluoroethane (R 134a) or 1,1,1,3,3-pentafluoropropane (R 245fa). Non-combustible blowing agent mixtures are preferably employed for the process according to the invention. Mixtures of 90 to 95 mol % R 365mfc with 5 to 10 mol % R 134a, for example, are particularly preferred. In another particularly preferred variant of the process according to the invention, mixtures of 40 to 95 mol %, preferably 40 to 60 mol %, and in particular 45 to 55 mol % R 365mfc with 5 to 60 mol %, preferably 40 to 60 mol %, and in particular 45 to 55 mol % R 245fa are employed.
As mentioned above, water is also additionally used as a blowing agent in the process according to the invention. The amount of water additionally incorporated into the polyurethane formulations is conventionally 0.05 to 0.6 parts by wt., preferably 0.1 to 0.4 parts by wt., per 100 parts by wt. of components b) and c) (polyol components). The amount of fluorohydrocarbon mixtures is 0.2 to 10 parts by wt., preferably 0.5 to 8 parts by wt., per 100 parts by wt. of components b), c), d) and e) or b) and d) or b), c) and d) or b), d) and e), depending on the particular composition of the reaction products.
Possible organic polyisocyanates a) are the aliphatic, cycloaliphatic, araliphatic and preferably aromatic polyfunctional isocyanates known per se, such as are mentioned, for example, in EP-A 364 854. The toluylene-diisocyanates and the diphenylmethane-diisocyanates, modification products thereof or their corresponding prepolymers, which can be modified by urethane, urea, biuret, allophanate, carbodiimide or uretdione groups, are particularly suitable. Aromatic polyisocyanates which are mentioned in particular are: 4,4-diphenylmethane-diisocyanate, mixtures of 2,4xe2x80x2- and/or 4,4xe2x80x2-diphenylmethane-diisocyanate or crude MDI types and/or 2,4- and/or 2,6-toluylene-diisocyanate and mixtures thereof with one another.
Suitable polyol components b) are those with an OH number of 20 to 200, prefrably 20 to 50, and a functionality of 2 to 6, preferably 2 to 3, corresponding polyether-polyols having a number-average molecular weight of 2,000 to 8,000 and corresponding polyester-polyols having a number-average molecular weight fo 2,000 to 4,000. Polyols with an OH number of 201 to 899 and a functionality of 2 to 3 can optionally be co-used as polyol component c). Polyols such as polyetherpolyols and polyesterpolyols, such as are obtained by addition of alkylene oxides, such as ethylene oxide and propylene oxide, on to polyfunctional starter molecules, such as ethylene glycol, propylene glycol, glycerol, trimethylopropane, sorbitol and/or ethylenediamine, or by condensation of dicarboxylic acids, such as adipic acid, succinic acid, glutaric acid, suberic acid, sebacic acid, maleic acid and phthalic acid, with predomiantly bifunctional hydroxy components, such as ethylene glycol, propylene glycol, built up from ethylene oxide and propylene oxide and glycerol, trimethylolpropane, ethyldiamine, propylene glycol, ethylene glycol, sorbitol and mixtures therof as starter molecules, have proved to be particularly suitable. Modified polyols such as are obtained as polyurea dispersions or as PIPA polyols by grafting of polyols with styrene and/or acrylonitrile, can also be used as polyol component b). The polyether and polyester polyols can be employed both individually and as a mixture with one another.
Those chain lengthening agents with an OH or amine number of 600 to 1,850 and a functionality of 2 to 4, in particular 2 to 3, are particularly suitable as component d). Examples which may be mentioned here are glycols, such as ethylene glycol, 1,4-butanediol, glycerol, trimethylolpropane and short-chain alkoxylation products thereof, as well as diethyltoluylenediamine isomers. The crosslinking agent component (chain lengthening component) d) is used in amounts of 3 to 20 wt. %, based on the sum of the amounts of polyol component b) and c) (if present), ethylene glycol and 1,4-butanediol being preferred as diols and diethyltoluylenediamine isomers being preferred as diamines.
Additives, activators and/or stabilizers known in principle to the expert can be employed as component e). These are, for example, compounds containing tertiary amino groups, such as 1,4-diazo[2,2,2]-bicyclooctane or bis(2-dimethylaminoethyl) ether, organometallic compounds, such as dimethyltin dilaurate or dibutyltin dilaurate, colour pastes, yellowing stabilizers, fillers, flameproofing agents, internal release agents or stabilizers such as are described in EP-A 364 854.
The amounts depend on the particular field of use and can be determined by preliminary experiments.
The production of the shaped articles according to the invention is also known to the expert and does not need to be described in more detail. In this connection, reference is again made to EP-A 364 854.
The flexible to semi-rigid polyurethane foams with an integral structure produced by the process according to the invention as a rule have Shore A hardnesses of between 30 and 90 in the edge zone and compressive strengths of between 30 and 350 kPa at bulk densities of between 150 and 900 kg/m3.
The combination of high surface hardnesses (in Shore A) with low compressive strengths of the shaped articles, which indicates a pronounced integral structure, is particularly advantageous in the integral foams produced by the process according to the invention.
Fields of use for the shaped articles according to the invention are e.g. bicycle saddles, safety valves, interior fittings of motor vehicles (arm rests, head rests, steering wheel sheathing), motorcycle seats, arm rests in the office furniture sector and treatment chairs in the medical sector.